The present invention relates to a spark plug having a housing, an insulator nose attached to the housing, a center electrode inserted through the insulator nose and projecting above the insulator nose tip, an intermediate electrode separated from the center electrode by a first spark gap, and a ground electrode attached to the housing.
Double-spark plugs of this type are described in German Patent No. 151 524.
Double-spark plugs that have two center electrodes also are described in German Patent No. 164 902.
Although it can be used for any spark plug, the present invention and its underlying principle are explained in relation to an on-board spark plug in the spark-ignition engine of a motor vehicle.
Generally speaking, the air/fuel mixture in the combustion chamber of each cylinder of the spark-ignition engine must be reliably ignited by the relevant spark plug with each combustion cycle to avoid misfiring, which could, for example, damage the catalytic converter.
Conventional spark plugs cannot guarantee reliable flame cone formation at high flow rates and in the case of mixture inhomogeneity, in particular in certain combustion chamber arrangements (for example, if the injection valve is oriented toward the spark plug). This problem can be overcome, for example, by increasing the igniting voltage at higher flow rates and in the case of mixture inhomogeneity. However, this procedure is complicated.
The spark plug according to the present invention has the advantage over conventional approaches in that flame cones are formed at two ignition sites using a single ignition operation. This greatly increases the probability of a reliable flame cone formation without requiring any additional measures.
According to the present invention, a solid-state insulating body, which forms a second spark gap in the form of a surface gap passing over the solid-state insulating body, is provided between the intermediate electrode and the ground electrode.
According to one example embodiment, the solid-state insulating body device is in the shape of a ring. Due to the ring symmetry, the second spark is advantageously formed on a surface gap that forms in the location of the lowest mixture flow rate, i.e., on the lee side.
According to a further example embodiment, the ground electrode, intermediate electrode, and solid-state insulating body form a largely flush transition surface on the outer ring surface of the solid-state insulating body, with the second spark gap in the form of the surface gap being provided on this transition surface. The advantage of this is that a spark does not form inside t-he spark plug, but rather only on the spark plug exterior.
According to another example embodiment, the ground electrode, intermediate electrode, and solid-state insulating body each form a shoulder on the inner ring surface of the solid-state insulating body, with the formation of the second spark gap in the form of the surface gap being limited by this shoulder.
According to another example embodiment, the ground electrode, intermediate electrode and solid-state insulating body form a largely flush transition surface on the outer ring surface and the inner ring surface of the solid-state insulating body, with the outer ring surface of the solid-state insulating body being narrower than the inner ring surface so that the second spark gap in the form of the surface gap passes along the outer ring surface.
According to another example embodiment, the ground electrode and/or the intermediate electrode can be screwed onto the solid-state insulating body. The advantage of this is that these components can be replaced.
According to another example embodiment, the ground electrode, intermediate electrode, and solid-state insulating body have a cylindrically symmetrical shape.
According to another example embodiment, the intermediate electrode has at least one intermediate electrode finger at which the first spark gap is aimed from the center electrode.
According to another example embodiment, the first spark gap is a spark gap in air.
According to another example embodiment, the first spark gap is a surface gap that passes at least partially over the insulator nose.
According to another example embodiment, a third spark gap is provided between the center electrode and the intermediate electrode, with either the first or the third spark gap being a spark gap in air and the other being a surface gap that passes at least partially over the insulator nose.
According to another example embodiment, at least one further intermediate electrode and one further corresponding solid-state insulating body are provided between the ground electrode and the solid-state insulating body.
According to another example embodiment, the solid-state insulating body is made of ceramic.